ORLANDO, Fla. -- Power executives were still in the dark Wednesday about how a glitch at a substation triggered a blackout that cut power to millions across south Florida, causing gridlock when traffic signals went dead, forcing hospitals to scramble for generators and cutting off air conditioners in the afternoon heat.

The sporadic outages Tuesday spanned 300 miles of the peninsula but appeared to be concentrated in the southeast portion of the state. Communities along the southwest coast, in the Florida Keys and as far north as Daytona Beach reported interruptions.

In Central Florida, outages were reported in Brevard, Lake, Orange, Osceola. Seminole and Volusia Counties. Most customers were restored by late afternoon.

Nuclear Plants Affected

The problem caused a nuclear plant south of Miami to automatically shut down. Authorities said there were no safety concerns at the Turkey Point nuclear plant but did not specify the outage's cause. While many areas were hit hard, the outages were short lived and only a few hundred thousand people lacked electricity for the evening commute home.

A Florida Power & Light spokesman initially said the nuclear plant caused the outages to about a fifth of Florida's population. But the utility's nuclear spokesman, Dick Winn, later said grid problems caused both reactors at the Turkey Point plant south of Miami to shut down between 1 p.m. and 1:30 p.m.

"All the safety systems worked just like they were supposed to and both of those units are in stable condition right now," he said.

Two other power plants farther north in the state, the Crystal River reactor and St. Lucie twin reactors, continued to operate, although officials at those two facilities noticed the grid disturbance.

Terrorism Not A Factor

The outages have no connection to terrorism, Homeland Security Department spokeswoman Laura Keehner said. No foul play was suspected, Miami-Dade County Mayor Carlos Alvarez said.

Outages Hit Millions

Florida emergency management officials said the outages cut power to about 2-3 million people, although FPL said the number was closer to 800,000.

FPL estimated power would be restored by 6 p.m. If residents do not have power at that time, they should call 1-800-4OUTAGE.

Report An Outage

The outages began shortly after 1p.m. Eastern time.

A Progress Energy spokesman said a loss of power from non-Progress units caused a shortage of electricity to its customers. An automated system kicked in that helps stabilize power statewide and that caused some of Progress' Central Florida customers to go dark. Progress expected most of its customers to have power back by 3p.m.

The Kissimmee Utilities Authority said more than 7,000 of its customers were affected but power was quickly restored to all of them.

Central Florida Hit In Early Afternoon

Reports to the Eyewitness News newsroom said power was off in parts of the downtown Orlando area for approximately 20 minutes Tuesday afternoon at about 1p.m. before coming back on. Winter Park officials say they went dark but power has since returned. Orange County Fire and Rescue reported outages from the near Disneyworld complex north to Apopka.

Orange County Schools lost power at Lake Sybelia, Riverside, Dommerich, Zellwood, Lake Weston, West Creek and East Lake elementary schools, Maitland and Hunter's Creek middle schools and Boone, Jones, Wekiva and Apopka high schools.

Brevard County schools without power included Indialantic, Columbia, and Freedom 7 elementary schools, Hoover and Stone middle schools, Edgewood Jr./Sr. high schools and Whispering Hills, Royal Palm and the South Area Adult Education Center.

CiCi's Pizza in Port Orange lost power for roughly two hours during their busy lunch rush.

"We told the customers that we were out of power and then they just left because we didn't have any ovens, any pizzas," manager Frances Cruz said. "We lost a lot of money today."

Police directed traffic in intersections in Daytona Beach where traffic lights stopped functioning. In Orlando, police said about 15 intersections went dark. Palm Bay police said the problems were mostly concentrated in the Southeast area along Babcock Street San Filippo, Foundation Parkway, Eldron, and Bayside Lakes. Election officials in Brevard County said power went out at a couple of polling sites in Tuesday's special election to replace resigned state representative Bob Allen but those outages were not expected to cause any problems.

Officials at Disneyworld said no key areas of its parks were affected. Disney has an agreement with the state of Florida that requires it to reduce usage where there is a major power issue. A Disney spokesperson said the complex reduced power to non-critical areas for about 20 minutes Tuesday afternoon.

At Orlando International Airport, a combination of the power outage and weather stopped departures between about 1p.m and 2p.m. The delay backed up about 30 flights. Melbourne International Airport reported no problems. An official at the Miami International Airport said the facility is working on a generator backup but that no airline delays were reported.

The Florida Institute of Technology in Melbourne cancelled Tuesday afternoon and evening classes.

Outage Started In South Florida

Outages were concentrated in the southeast portion of the state, including Miami, but were also reported in the southwestern and northeastern parts of the state as well as in the Florida Keys. The outages began shortly after 1 p.m., though power in some affected areas had been restored an hour later.

Jaime Hernandez, a spokesman for Miami-Dade County Department of Emergency Management, said no injuries have been reported so far. Officials said Miami International Airport, the Port of Miami and the area's rail and bus transportation were working normally.

Several Miami-area hospitals switched to backup generators when the power went out. Miami-Dade schools were scheduled to be dismissed on time, and officials said school buses would be running.

By 2 p.m., most of northern downtown Miami appeared to be back to normal operation, including a campus of Miami Dade College and numerous stores and businesses. Traffic lights were out for a short time but appeared to be back in regular operation. In the Florida Keys, spokesman Andy Newman said areas were without power for about 15 minutes, but it was back up as well.

Turkey Point Background

The first of Turkey Point's two nuclear power units started operation in 1972. In March 2006, a tiny hole was found in a coolant pipe at the plant. The FBI determined it was vandalism, not sabotage. An out-of-state contractor hired to do routine maintenance was suspected of drilling the hole, the FBI said at the time. The public's health and safety were not at risk, the Nuclear Regulatory Commission said then.